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DRV8840: DRV8840 is protected while the connection of motor winding is broken

Gavin Jiang
Intellectual 1470 points
Part Number: DRV8840

Dears,

I am using DRV8840 to drive an DC motor, the working current is about 1A. And we found that the DRV8840 will enter a protect and need reset to re-enable, it seems to be OCP. But from the waveform of the output current, It should not over current.

Is there any solution to prevent this OCP? We need to reverse the motor soon without reset DRV8840 device. thanks.

The Sch and current wave form please see below

  • 0
    TI__Guru** 114905 points
    Hi Gavin,

    Would you also provide the OUT1 and OUT2 voltages?

    What is the bulk capacitance of VM?

    Please try adding a 0.1uF capacitor in parallel with the sense resistor R15.
  • 0 in reply to Rick Duncan
    TI__Intellectual 1470 points
    Hi Rick,
    thanks a lot for you quick reply.
    I see the VM is connect to 24V VCC, with a 104/50V capacitor to GND from the sch. I assume the voltage of OUT1 and OUT2 is about to 24V.
    I will test the voltage of OUT1 and back to you tomorrow.
  • 0 in reply to Gavin Jiang
    TI__Guru** 114905 points
    Hi Gavin,

    There should be a large bulk capacitor on the board. Please see the DRV8840EVM as an example. The EVM has a 100uF capacitor (C7) used for bulk. Also there is a 0.1uF capacitor placed at each VM pin.
  • 0 in reply to Rick Duncan
    TI__Intellectual 1470 points

    Hi Rick,

    The voltage of OUT is 24V, the same with VM voltage.

    Today, I test it again. I added 220uF capacitor parallel with 0.1uF capacitor at each VM pin; Add one 0.1uF capacitor to R15(R sense);  I still got the OCP while the connection of motor winding is broken. 

    When I added some load to the motor, it will increase the current of motor winding ( the current of motor winding is 3A while it is 1.5A before). It is much easier to get OCP.  

    I don't know why I got the OCP?  the current of  OUT1 to OUT2 is very clear wit no rush current at the moment of "connection broken". you can see the photos as below.

    Another strange thing confusing me a lot is that, I got a reverse current when I turn ENBL from 1 to 0 (SLOW DECAY). And the reverse current up to 6.8A, with NO OCP. you can see below photos.